The invention relates to the field of nanoscale resolution, and in particular to a technique of achieving nanoscale resolution in three dimensions using light.
Patterning in three dimensions has important applications in photonic devices and micromachines. Three dimensional (3-D) micro- and nanostructures have been traditionally patterned via a layer-by-layer approach. The 3-D pattern is broken up into a series of 2-D layers, which are then overlaid on top of each other. Besides being extremely time-consuming, such approaches require very accurate overlay capabilities. Modifications to this approach via foldable and stackable membranes have also been proposed. However, the fundamental limitations still remain.
An alternative approach for 3-D nanopatterning involves 2-photon or multi-photon processes. These require extremely high light intensities. It has been difficult to achieve nanoscale resolution using multi-photon approaches because the conventional photopolymers almost always work in the UV (˜350 nm), which implies that 2 photons in the near IR (−700 nm) are required to initiate the 2-photon polymerization. The achievable resolution is given by the conventional far-field diffraction limit divided by square root of the number of photons involved. So, for a two-photon process, the minimum feature size or resolution is given by:
                              W          min                =                              k            1                    ⁢                      λ            NA                    ×                      1                          2                                                          Eq        .                                  ⁢        1            The improvement in resolution by √2 is effectively cancelled by the 2-fold increase in wavelength. The achievable resolution in this case is limited to several hundred nanometers.